Rapid growth of the portable electronics industry has led to increased demand for batteries, while a rise of internal temperature of the batteries raises a great deal of problems. Typical problems associated with elevation of temperature inside the battery will be reviewed hereinafter.
For example, generation of heat upon charge/discharge of the battery under normal operating conditions leads to operation of the battery at a temperature higher than the outside thereof. Consequently, occurrence of such a high temperature during operation of the battery results in rapid degradation of the battery. Further, rapid elevation in internal temperature of the battery under abnormal operating conditions is a leading cause of battery explosion.
Even though heat generation within a certain limit may be of help to operation of the battery, temperatures outside a specific range and a rapid increase of battery temperature are undesirable in terms of service life and safety of the battery.
As attempts to solve such problems, various methods have been developed which involve incorporation of flame retardants into certain structural elements of the battery, or induces hardening of electrolytes when the battery temperature is higher than a certain temperature, in order to prevent the risk of battery explosion due to sudden increases in temperature of the battery. However, these methods may be employed as measures capable of preventing battery explosion under abnormal operation states, but are not designed to inhibit temperature elevation during normal battery operation. Further, these methods are disadvantageous in that the state of the battery is changed into irreversible state and therefore the battery cannot be used any longer.
As such, there is an urgent need for development of techniques capable of prolonging the service life of the battery by inhibiting temperature elevation inside the battery under normal operating conditions or at least lowering an elevation rate of temperature, and capable of further improving safety of the battery by inhibiting rapid increase of the battery temperature.
Meanwhile, there are known techniques utilizing materials having high latent heat of phase change or phase transfer which are designed for certain applications. For instance, a technique is known which applies high-latent heat materials to garments, furnishings or the like so as to induce gentle temperature changes therein, in spite of rapid temperature changes in the outside, thereby providing more comfortable environment.
In addition, some techniques, in which such high latent heat characteristics are applied to batteries, are also known in the related art. For instance, in order to prevent adverse effects on humans by inhibiting rapid temperature elevation of a battery as a power source in implantable medical devices, International Publication No. WO 03/061032 has proposed a method of installing a battery in a housing including a high-latent heat material, a method in which the high-latent heat material is inserted in the form of heat absorbing mass inside a battery case, and a method in which the battery is assembled by inserting the high-latent heat material between a cathode sheet, an anode sheet and a separator sheet in the form of network-like endothermic mass. However, methods involving inserting the latent heat material, in the form of separate heat absorbing mass or network-like mass, into the interior of the battery case results in disadvantages such as increased size and deteriorated performance of the battery. As a result, there remains a need in the art for development of technology capable of solving such problems associated with battery size and performance together with temperature elevation inside the battery as mentioned above.